Data logging systems are available for a variety of applications. For example, image data from a surveillance camera may be inspected real-time by, for example security personnel, but is generally additionally, or alternatively, also logged into an image logging system or an off-line archive. As another example, in a so-called black box application in a vehicle such as an air plane, a train, a bus, a truck, a car, or any other vehicle, data relating to the vehicle's position, the vehicle's operational conditions, the vehicle's technical condition, sound and/or video recording data from a vehicle's cabin, sound and/or video recording data from a vehicle's passenger compartment, sound and/or video recording data from communication with e.g. traffic control, environmental conditions, road conditions, and/or alike may be recorded and logged into a black box memory. Some types of black boxes may also be referred to as a flight recorder, which is an alternative name for an electronic recording device placed in an aircraft for the purpose of facilitating the investigation of aviation accidents and incidents. There are two common types of flight recorders: the Flight Data Recorder (FDR) and the Cockpit Voice Recorder (CVR). A Flight Data Recorder (FDR) (also ADR, for accident data recorder) is an electronic device employed to record any instructions sent to any electronic systems on an aircraft. It is a device used to record specific aircraft performance parameters. Another kind of flight recorder is the Cockpit Voice Recorder (CVR), which records conversation in the cockpit, radio communications between the cockpit crew and others (including conversation with air traffic control personnel), as well as ambient sounds. In some black boxes, both functions have been combined into a single unit.
As described in, for example, United States Patent Application US 2005/0271251 A1, many surveillance systems record and store surveillance footage to video tape or other medium for future reference and analysis. With the advent of digital storage, it is possible to store video footage to a wide variety of digital storage devices, such as computer hard drives, optical disks and electronic non-volatile storage medium such as flash memory. In those systems that record video footage, all footage produced by a surveillance camera is typically stored in its entirety. The digital files generated by a video camera are very large and require a great deal of storage space. In addition, in order for a surveillance system to fully monitor an area, multiple cameras are generally required. There is a trend that the number of cameras in a surveillance system increases while the amount of video data that is to be stored also increases. In order to accommodate these storage requirements, many current surveillance system architectures make use of video archives that roll over after a certain timeframe. For example, a system may include a set of video tapes or computer disks that can store two months' worth of continuous surveillance data. For two months, surveillance data is sequentially written to the set of tapes or disks until the set is full. At this point, the set of tapes or disks is re-used, starting with the first tape or disk that contains the oldest data. Any new video surveillance data is then stored on the first tape or disk in the set, overwriting the old surveillance data. Obviously, older surveillance video data, which may still have value, is lost in a system that performs rollover storage. Alternatively, some systems back up or archive all video data wholesale to archival media once the data has become “stale.” That is, all data captured by the surveillance system is archived after a set period of time passes after the data is captured. In these systems, once data has been archived, it is no longer readily available to a user of the system. The archival media must be identified and loaded in order to view or obtain information about a particular event caught by surveillance video. Typically in these systems, all data is archived, and any data that is archived remains on the archival media permanently.
United States Patent Application US 2005/0271251 A1 describes methods of managing video data storage in a video surveillance system to extend the amount of calendar time for which video and image data can be stored on a storage device. The disclosed methods apply decision criteria, such as rules, configuration data and preferences, to support intelligent automatic reduction of stored surveillance data such that images and video data of most interest are maintained while less important data is deleted, compressed or archived. According to US 2005/0271251 A1, the method described therein can be applied to all data stored in a surveillance system such as, for example, video data, audio data, images, or metadata. This intelligent data reduction frees up space on surveillance video storage devices-effectively substantially extending the amount of calendar time that can be stored on a storage device of a given size compared to other current systems. According to US 2005/0271251 A1, the techniques described therein provide for managing video data storage in a video surveillance system by obtaining data storage management rules from a user and applying the rules to the stored video data. The data storage management rules include data storage rules and data importance assessment rules. The video data generated by the video surveillance system is stored in accordance with the data storage rules, and video data storage is automatically updated in accordance with the data storage rules and the data importance assessment rules.
However, prior art methods like the methods described in US 2005/0271251 A1 rely on data storage management rules include data storage rules and data importance assessment rules obtained from a user, and techniques like significant event determination, assessing the value of detected events, types of events, object recognition process, and other techniques to support intelligent automatic reduction. Such intelligent techniques may however result in an incorrect assessment of data importance, in which case possibly important data may not be logged even though a vast amount of non-relevant data may be present. Further, for certain type of data in some applications, it may be difficult for a user to define data storage rules and data importance assessment rules, or not wishful. For example, in some black box application, it may not be acceptable by the relevant authority that data logging decisions are made by applying data storage rules and data importance assessment rules obtained from a user that may not be robust against non-foreseeable situations, such as accidents of unknown types. It may for example be difficult to define data storage rules and data importance assessment rules supporting uncompromised storage of data prior to an event that may occur at an unexpected moment in the future.